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// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/handles/handles.h"
#include "src/api/api.h"
#include "src/base/logging.h"
#include "src/handles/maybe-handles.h"
#include "src/objects/objects-inl.h"
#include "src/roots/roots-inl.h"
#include "src/utils/address-map.h"
#include "src/utils/identity-map.h"
#ifdef DEBUG
// For GetIsolateFromWritableHeapObject.
#include "src/heap/heap-write-barrier-inl.h"
#endif
namespace v8 {
namespace internal {
// Handles should be trivially copyable so that they can be efficiently passed
// by value. If they are not trivially copyable, they cannot be passed in
// registers.
ASSERT_TRIVIALLY_COPYABLE(HandleBase);
ASSERT_TRIVIALLY_COPYABLE(Handle<Object>);
ASSERT_TRIVIALLY_COPYABLE(MaybeHandle<Object>);
#ifdef DEBUG
bool HandleBase::IsDereferenceAllowed() const {
DCHECK_NOT_NULL(location_);
Object object(*location_);
if (object.IsSmi()) return true;
HeapObject heap_object = HeapObject::cast(object);
if (IsReadOnlyHeapObject(heap_object)) return true;
Isolate* isolate = GetIsolateFromWritableObject(heap_object);
RootIndex root_index;
if (isolate->roots_table().IsRootHandleLocation(location_, &root_index) &&
RootsTable::IsImmortalImmovable(root_index)) {
return true;
}
return AllowHandleDereference::IsAllowed();
}
#endif
int HandleScope::NumberOfHandles(Isolate* isolate) {
HandleScopeImplementer* impl = isolate->handle_scope_implementer();
int n = static_cast<int>(impl->blocks()->size());
if (n == 0) return 0;
return ((n - 1) * kHandleBlockSize) +
static_cast<int>(
(isolate->handle_scope_data()->next - impl->blocks()->back()));
}
Address* HandleScope::Extend(Isolate* isolate) {
HandleScopeData* current = isolate->handle_scope_data();
Address* result = current->next;
DCHECK(result == current->limit);
// Make sure there's at least one scope on the stack and that the
// top of the scope stack isn't a barrier.
if (!Utils::ApiCheck(current->level != current->sealed_level,
"v8::HandleScope::CreateHandle()",
"Cannot create a handle without a HandleScope")) {
return nullptr;
}
HandleScopeImplementer* impl = isolate->handle_scope_implementer();
// If there's more room in the last block, we use that. This is used
// for fast creation of scopes after scope barriers.
if (!impl->blocks()->empty()) {
Address* limit = &impl->blocks()->back()[kHandleBlockSize];
if (current->limit != limit) {
current->limit = limit;
DCHECK_LT(limit - current->next, kHandleBlockSize);
}
}
// If we still haven't found a slot for the handle, we extend the
// current handle scope by allocating a new handle block.
if (result == current->limit) {
// If there's a spare block, use it for growing the current scope.
result = impl->GetSpareOrNewBlock();
// Add the extension to the global list of blocks, but count the
// extension as part of the current scope.
impl->blocks()->push_back(result);
current->limit = &result[kHandleBlockSize];
}
return result;
}
void HandleScope::DeleteExtensions(Isolate* isolate) {
HandleScopeData* current = isolate->handle_scope_data();
isolate->handle_scope_implementer()->DeleteExtensions(current->limit);
}
#ifdef ENABLE_HANDLE_ZAPPING
void HandleScope::ZapRange(Address* start, Address* end) {
DCHECK_LE(end - start, kHandleBlockSize);
for (Address* p = start; p != end; p++) {
*p = static_cast<Address>(kHandleZapValue);
}
}
#endif
Address HandleScope::current_level_address(Isolate* isolate) {
return reinterpret_cast<Address>(&isolate->handle_scope_data()->level);
}
Address HandleScope::current_next_address(Isolate* isolate) {
return reinterpret_cast<Address>(&isolate->handle_scope_data()->next);
}
Address HandleScope::current_limit_address(Isolate* isolate) {
return reinterpret_cast<Address>(&isolate->handle_scope_data()->limit);
}
CanonicalHandleScope::CanonicalHandleScope(Isolate* isolate)
: isolate_(isolate), zone_(isolate->allocator(), ZONE_NAME) {
HandleScopeData* handle_scope_data = isolate_->handle_scope_data();
prev_canonical_scope_ = handle_scope_data->canonical_scope;
handle_scope_data->canonical_scope = this;
root_index_map_ = new RootIndexMap(isolate);
identity_map_ = new IdentityMap<Address*, ZoneAllocationPolicy>(
isolate->heap(), ZoneAllocationPolicy(&zone_));
canonical_level_ = handle_scope_data->level;
}
CanonicalHandleScope::~CanonicalHandleScope() {
delete root_index_map_;
delete identity_map_;
isolate_->handle_scope_data()->canonical_scope = prev_canonical_scope_;
}
Address* CanonicalHandleScope::Lookup(Address object) {
DCHECK_LE(canonical_level_, isolate_->handle_scope_data()->level);
if (isolate_->handle_scope_data()->level != canonical_level_) {
// We are in an inner handle scope. Do not canonicalize since we will leave
// this handle scope while still being in the canonical scope.
return HandleScope::CreateHandle(isolate_, object);
}
if (Internals::HasHeapObjectTag(object)) {
RootIndex root_index;
if (root_index_map_->Lookup(object, &root_index)) {
return isolate_->root_handle(root_index).location();
}
}
Address** entry = identity_map_->Get(Object(object));
if (*entry == nullptr) {
// Allocate new handle location.
*entry = HandleScope::CreateHandle(isolate_, object);
}
return *entry;
}
DeferredHandleScope::DeferredHandleScope(Isolate* isolate)
: impl_(isolate->handle_scope_implementer()) {
impl_->BeginDeferredScope();
HandleScopeData* data = impl_->isolate()->handle_scope_data();
Address* new_next = impl_->GetSpareOrNewBlock();
Address* new_limit = &new_next[kHandleBlockSize];
// Check that at least one HandleScope with at least one Handle in it exists,
// see the class description.
DCHECK(!impl_->blocks()->empty());
// Check that we are not in a SealedHandleScope.
DCHECK(data->limit == &impl_->blocks()->back()[kHandleBlockSize]);
impl_->blocks()->push_back(new_next);
#ifdef DEBUG
prev_level_ = data->level;
#endif
data->level++;
prev_limit_ = data->limit;
prev_next_ = data->next;
data->next = new_next;
data->limit = new_limit;
}
DeferredHandleScope::~DeferredHandleScope() {
DCHECK(handles_detached_);
impl_->isolate()->handle_scope_data()->level--;
DCHECK_EQ(impl_->isolate()->handle_scope_data()->level, prev_level_);
}
std::unique_ptr<DeferredHandles> DeferredHandleScope::Detach() {
std::unique_ptr<DeferredHandles> deferred = impl_->Detach(prev_limit_);
HandleScopeData* data = impl_->isolate()->handle_scope_data();
data->next = prev_next_;
data->limit = prev_limit_;
#ifdef DEBUG
handles_detached_ = true;
#endif
return deferred;
}
} // namespace internal
} // namespace v8
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